Process for purifying and recovering contaminated catalyst solution obtained in the carbonylation of methyl acetate and/or dimethylether

ABSTRACT

The disclosure relates to a process for purifying and recovering a contaminated catalyst solution which is obtained in the carbonylation of methyl acetate and/or dimethylether, the catalyst solution containing carbonyl complexes of noble metals of group VIII of the Periodic System of the elements, quaternary heterocyclic aromatic nitrogen compounds or quaternary organophosphorus compounds as organic promoters, undistillable organic contaminants as well as acetic acid, acetic anhydride and ethylidene diacetate. To this end, the disclosure provides for the catalyst solution to be distillatively freed from its volatile constituents and for the remaining solid distillation residue to be water-treated, the noble metal/carbonyl-complex being precipitated together with the organic contaminants and the organic promoter becoming dissolved; for the precipitated and contaminated noble metal/carbonyl-complex to be removed by filtration and for the noble metal to be recovered terefrom in known fashion; for the organic promoter to be recovered by evaporating the water or extracting it with halogenated hydrocarbons and for these latter to be evaporated.

The present invention relates to a process for purifying and recoveringa contaminated catalyst solution which is obtained in the carbonylationof methyl acetate and/or dimethylether, the catalyst solution containingcarbonyl complexes of noble metals of group VIII of the Periodic Systemof the elements, quaternary heterocyclic aromatic nitrogen compounds orquaternary organophosphorus compounds as organic promoters,undistillable organic contaminants as well as acetic acid, aceticanhydride and ethylidene diacetate.

The recovery of rhodium or rhodium carbonyl complexes from catalystsystems contaminated with residues or from distillation residues hasalready been described, basically in connection with hydroformylationprocesses. The process described in DE-PS No. 12 90 535, for example,provides for rhodium-containing hydroformylation residue to be treatedwith an aqueous organic acid, the rhodium complex becoming dissolved andseparated from the organic phase, rhodium being recovered in a yield of82 up to 94%.

The process described in DE-AS No. 12 95 537 provides for therhodium-containing reaction residue to be treated with steam under apressure of 2 to 31 bars at 100° to 250° C. The catalyst becomesdecomposed and rhodium sludge, which as such cannot be used again in thecarbonylation reaction, is recovered by filtration under pressure.

Further processes for recovering rhodium and or regenerating catalysthave been described in DE-OS No. 24 48 005 and DE-OS No. 26 14 799. Asdisclosed therein, the contaminated distillation residues originatingfrom hydroformylation reactions are subjected initially to treatmentwith oxygen-containing mineral acids and peroxides, the treatment beingintended to destroy rhodium and iridium carbonyl complexes and degradethe residues. After decomposition of peroxides in excess, the aqueousmetal salt solutions are worked up by different methods. One of suchmethod described in DE-OS No. 24 48 005 provides for the aqueous rhodiumor iridium salt solution to be admixed at 0° up to 150° C. under apressure of 1 up to 250 bars with a water soluble organic solvent, ahydrohalic acid or an alkali metal halide and a tertiary phosphine, andfor the metals to be precipitated from the solution in the form ofrhodium or iridium-carbonyl complexes with the use of carbon monoxideand additionally under hydrating conditions. As disclosed in DE-OS No.26 14 799, rhodium⁺⁺⁺ is first absorbed from the aqueous solution on acation exchanger and then desorbed by means of hydrochloric acid. Thehydrochloric acid solution is admixed with tertiary phosphines, treatedwith CO and, if desired, hydrogen, and rhodium is precipitated as acarbonyl complex.

The processes described, for example, in DE-OS No. 24 50 965 and 28 36084 are, however, not of assistance in the purification and recovery ofnoble metal carbonyl-complexes (Rh, Ir, Pd, Ru) and their promoters fromthe contaminated catalyst solutions obtained in the carbonylation ofmethyl acetate or dimethylether. The catalyst solution obtained in thecarbonylation reaction is composed of 0.1 up to 10 weight % noblemetal/carbonyl complex, 40-70 weight % organic promoter, 1-10 weight %undistillable organic contaminants, and 20-40 weight % acetic acid,acetic anhydride and ethylidene diacetate. As can be inferred from thecomposition just indicated, it is possible for the catalyst solution tocontain up to 80 weight % undistillable substances. After removal ofvolatile constituents by distillation, it is naturally possible tosubject the noble metal/carbonyl-complex to oxidative degradation butthis would entail the destruction of the entire quantity of organicpromoters whereby the beneficial effect which is associated withcatalyst work up would be jeopardized from the onset.

Subjecting the residue to treatment with aqueous organic acids alsoentails adverse effects as the noble metal/carbonyl-complex undergoessolution as well as the bulk of undistillable organic contaminants,which then cannot be separated from catalyst and promoter.

On subjecting the catalyst to decomposition with steam at elevatedtemperature, noble metal in elementary form is obtained. At the sametime, water-insoluble organic residue which cannot readily be separatedfrom the elementary noble metal is obtained.

The present invention which enables the adverse effects describedhereinabove to be avoided now provides a process wherein distillativeoperation and, if desired, extractive operation permit catalyst solutionwhich is used and gradually contaminated in the carbonylation of methylacetate and/or dimethylether to be worked up in such a manner that it ispossible for the organic promoters to be used again in the catalystcycle, undistillable organic contaminants being removed and noble metalbeing recovered therefrom. The present process compares favorably withthe work-up methods described heretofore inasmuch as the extractantsused for effecting work-up are cycled, pollution of the environment bywaste material being substantially avoided. Only those undistillableorganic contaminants which are formed during the process and reactionare removed for disposal by incineration, for example, in accordancewith pertinent art.

The present process comprises more particularly: distillatively freeingthe catalyst solution from its volatile constituents and water-treatingthe remaining solid distillation residue, the noblemetal/carbonyl-complex being precipitated together with the organiccontaminants and the organic promoter becoming dissolved; removing theprecipitated and contaminated noble metal/carbonyl-complex by filtrationand recovering the noble metal in known manner therefrom; recovering theorganic promoter by evaporating the water or extracting it withhalogenated hydrocarbons and evaporating these latter.

Further preferred features of the present invention provide:

(a) for the distillation residue to be water treated at 40° to 80° C.;

(b) for 10 to 100 parts by weight water to be used per part by weightdistillation residue;

(c) for the quaternary organophosphorus compounds to be recovered fromtheir aqueous solution by extraction with methylene chloride orchloroform.

With respect to the origin of the contaminated catalyst solution, it isinteresting to state that the reaction mixture coming from thecarbonylation reactor is separated distillatively into desirable finalproducts, especially acetic anhydride, acetic acid and/or ethylidenediacetate, and unreacted cycled feed material on the one hand, and intocatalyst solution as base material on the other hand. A portion of thiscatalyst solution which becomes gradually contaminated is taken from thecatalyst solution cycle and distillatively freed in accordance with thisinvention, preferably at 100°-120° C. and 1-100 millibars from volatilematter, e.g. acetic acid, acetic anhydride and ethylidene diacetate.

The noble metals customarily contained in the contaminated catalystsolutions comprise rhodium, iridium, palladium and/or ruthenium whichare present as carbonyl complexes e.g. of the formula [CH₃ P(C₄ H₉)₃ ]²Rh(CO)I₅ or CH₃ P(C₄ H₉)₃ Rh(CO)₂ I₂. As organic promoters, the catalystsolutions generally contain one or more of the following heterocyclicaromatic nitrogen compounds or organophosphorus compounds:

(1) N-methylpyridinium iodide; N,N-dimethylimidazolium iodide;N-methyl-3-picolinium iodide; N-methyl-2,4-lutidinium iodide;N-methyl-3,4-lutidinium iodide, N-methyl-quinolinium iodide;

(2) tri-n-butyl-methyl-phosphonium iodide; trioctyl-methyl-phosphoniumiodide; trilauryl-methyl-phosphonium iodide;triphenyl-methyl-phosphonium iodide.

Next, the distillation residue which remains behind should beintroduced, preferably with agitation, into water and heated to 70° C.,for example. The organic promoter portion contained in the distillationresidue becomes dissolved in the water phase, whilst the noblemetal/carbonyl complex and the undistillable organic contaminants formedduring the reaction remain undissolved. Residue insoluble in the waterphase is filtered off and should be delivered to a refinery forseparation of the organic contaminants and recovery of the pure noblemetal as such or as compound, in known fashion.

The promoter dissolved in the water phase is recovered in the form ofpure material, after evaporation of the water, and used again in thereaction. In the event of the organic promoters being selected fromquaternary organophosphorus compounds, it is possible for the organicpromoter which is dissolved in the water phase to be also extracted withthe use of halogenated hydrocarbons. This naturally means an economy ofthe expenses incurred by the evaporation of water. After evaporation ofthe extractant, pure organic promoter is obtained which is recycled tothe catalyst solution cycle. The water raffinate is freed from thedissolved halogenated hydrocarbon by stripping. Next, water phase andhalogenated hydrocarbons can be used again. Needless to say, the processof this invention can be carried out continuously or discontinuously.

EXAMPLE 1

250 g catalyst solution cycled for methyl acetate carbonylation wastaken from the catalyst cycle consisting of rhodium carbonyl complex (L₂Rh(CO)I₅ ; L=ligand), tri-n-butylmethylphosphonium iodide as an organicpromoter, acetic anhydride, acetic acid, ethylidene diacetate, andorganic contaminants and freed from distillable materials under reducedpressure of about 2 millibars and at a base temperature of up to 120° C.81.5 g (32.6 weight %) distillate (25.8 weight % acetic acid, 73.8weight % acetic anhydride and 0.4 weight % ethylidene diacetate) and168.5 g distillation residue containing 0.433 g rhodium and 145.71 gtri-n-butylmethylphosphonium iodide (=2 weight % Rh-carbonyl complex and58.3 weight % TBMPI, based on 250 g catalyst solution) were obtained.The distillation residue was placed in a mortar, comminuted therein andthen introduced with vigorous agitation into 5000 ml water at 20°-25° C.After 30 minutes, the suspension was heated to 60°-70° C. whileagitation was continued. After altogether 1.5 hours, the residue wasfiltered, after-washed with water and dried for 1.5 hours at 120° C.under 2 millibars. 22.75 g material was weighed.

The water phase originating from the filtration was worked up underreduced pressure and 145.5 g tri-n-butyl-methylphosphonium iodide,corresponding to a yield of 99.8%, was obtained as distillation residue.P/I-analysis with the use of 9 weight % P and 36.9 weight % iodine aswell as IR-analysis and the melting point of 140° C. evidenced that thesalt recovered was very pure. The presence of rhodium could here not beevidenced by analysis. The organic promoter salt as such was used againin the process and the water phase evaporated was used again forextraction.

EXAMPLE 2

250 g catalyst solution cycled for dimethylether carbonylation was takenfrom the catalyst cycle consisting of acetic anhydride, acetic acid,ethylidene diacetate, rhodium carbonyl complex (LRh(CO)₂ I₂ ; L=ligand),tri-n-butylmethylphosphonium iodide and undistillable organiccontaminants, and freed from distillable matter under reduced pressureof 2 millibars at a base temperature of 120° C. 72 g (28.8 weight %)distillate, (31 weight % acetic acid, 68.6 weight % acetic anhydride and0.4 weight % ethylidene diacetate) and 178 g distillation residuecontaining 1.718 g rhodium and 156.3 g tri-n-butylmethylphosphoniumiodide (=4.35 weight % Rh-carbonyl complex and 62.5 weight % TBMPI,based on 250 g catalyst solution) were obtained. The distillationresidue was ground and introduced, with agitation, into 6000 ml water at20° C. After 30 minutes, the suspension was heated to 60°-70° C. whileagitation was continued. After altogether 1.5 hours, the remainingresidue was filtered, after-washed with water and dried at 120° C. undera pressure of 2 millibars. 21.75 g material was weighed. It was analyzedand found to contain 1.718 g rhodium.

The water phase obtained by filtration was shaken 6 times, each timewith 250 ml chloroform, for recovering the organic promoter. Afterevaporation of the chloroform, 156 g tri-n-butylmethylphosphoniumiodide, corresponding to a yield of 99.8%, was obtained from thechloroform phase. P/I-analysis with 9 weight % phosphorus and 36.9weight % iodine, IR-analysis and melting point indicated that theorganic promoter salt recovered was very pure. The extracted water phasewas freed from dissolved chloroform by stripping and could be usedagain. The chloroform was used in further operations for extractingorganic promoter.

Instead of extracting the promoter dissolved in the water phase byshaking with chloroform, it is naturally possible for it to be extractedcontinuously with the use of a multiple stage column.

EXAMPLE 3

250 g catalyst solution cycled for methyl acetate carbonylation wastaken from the catalyst cycle consisting of rhodium carbonyl complex (L₂Rh(CO)I₅ ; L=ligand), N,N-dimethylimidazolium iodide, undistillableorganic contaminants, acetic acid, acetic anhydride and ethylidenediacetate, and freed from distillable matter under a reduced pressure of2 millibars and a base temperature of up to 120° C. 64 g (25.6 weight %)distillate (29.3 weight % acetic acid, 70.3 weight % acetic anhydrideand 0.4 weight % ethylidene diacetate) and 186 g distillation residuewhich contained 0.525 g rhodium and 161 g N,N-dimethylimidazolium iodide(=1.96 weight % Rh-carbonyl complex and 64.4 weight % DMII, based on 250g catalyst solution) were obtained. The distillation residue wascomminuted and introduced with agitation into 4500 ml water at 20° C.After 30 minutes, the suspension was heated to 60°-70° C. whileagitation was continued. After altogether 1.5 hours, the remainingresidue was filtered, after-washed with water and dried at 120° C. under2 millibars. 25 g weighed material was obtained. Analysis indicated thatit contained 0.525 g rhodium.

The water phase originating from the filtration was worked up underreduced pressure so as to recover the organic promoter. Afterevaporation of the water, 160.5 g N,N-dimethylimidazolium iodide,corresponding to a yield of 99.7%, was obtained. N/I-analysis with 12.5weight % N and 56.7 weight % iodine and IR-analysis indicated that theorganic promoter salt recovered was very pure. The organic promoter saltwas recycled into the reaction and the water distilled off was usedagain for extraction.

EXAMPLE 4

250 g catalyst solution cycled for methyl acetate carbonylation wastaken from the catalyst cycle consisting of palladium carbonyl complex,tri-n-butylmethylphosphonium iodide as organic promoter, undistillableorganic contaminants, acetic acid, acetic anhydride and ethylidenediacetate, and freed from distillable matter at a base temperature of upto 120° C. and under a reduced pressure of 2 millibars. 80 g (32 weight%) distillate (51.9 weight % acetic acid, 10 weight % acetic anhydrideand 38.1 weight % ethylidene diacetate) and 170 g distillation residuecontaining 0.85 g palladium and 152 g tri-n-butyl-methylphosphoniumiodide (=2 weight % Pd-carbonyl complex and 60.8 weight % TBMPI, basedon 250 g catalyst solution) were obtained. The distillation residue wascomminuted and introduced with agitation into 5000 ml water at 20° C.After 30 minutes, the suspension was heated to 65° C. while agitationwas continued. After altogether 1.5 h, the residue was filtered,after-washed with water and dried at 120° C. under 2 millibars. 18 gweighed material which contained 0.846 g palladium was obtained.

The water phase originating from the filtration was worked up underreduced pressure to recover the organic promoter. After evaporation ofthe water, 151 g tri-n-butylmethylphosphonium iodide, corresponding to ayield of 99.3%, was obtained. The organic promoter salt was recycled tothe carbonylation reaction and the water distilled off was used againfor extraction.

We claim:
 1. In a process for purifying and recovering constituents froma contaminated catalyst solution which is obtained as a result of thecarbonylation of methyl acetate, dimethylether, or a mixture ofmethylacetate and dimethyl ether, the contaminated catalyst solutioncontaining carbonyl compounds of noble metals of group VIII of thePeriodic System of the elements, quaternary heterocyclic aromaticnitrogen compounds or quaternary organophosphorus compounds as organicpromoters, undistillable organic contaminants, and volatileconstituents, including acetic acid, acetic anhydride and ethylidenediacetate, the improvement which comprises: distillatively freeing thecatalyst solution from the volatile constituents and water-treating theremaining solid distillation residue, the noble metal/carbonyl-compoundbeing thereby precipitated together with the organic contaminants andthe organic promoter becoming dissolved in water; removing theprecipitated and contaminated noble metal/carbonyl-compound byfiltration; recovering the noble metal therefrom; and recovering theorganic promoter by evaporating the water.
 2. A process as claimed inclaim 1 wherein the distillation residue is water treated at 40° to 80°C.
 3. A process as claimed in claim 1 wherein 10 to 100 parts by weightwater are used per part by weight distillation residue.
 4. In a processfor purifying and recovering constituents from a contaminated catalystsolution which is obtained as a result of the carbonylation of methylacetate, dimethylether, or a mixture of methylacetate and dimethylether,the contaminated catalyst solution containing carbonyl compounds ofnoble metals of group VIII of the Periodic System of the elements,quaternary heterocyclic aromatic nitrogen compounds or quaternaryorganophosphorus compounds as organic promoters, undistillable organiccontaminants, and volatile constituents including acetic acid, aceticanhydride and ethylidene diacetate, the improvement which comprises:distillatively freeing the catalyst solution from the volatileconstituents and water-treating the remaining solid distillationresidue, the noble metal/carbonyl-compound being thereby precipitatedtogether with the organic contaminants and the organic promoter becomingdissolved in water; removing the precipitated and contaminated noblemetal/carbonyl-compound by filtration; recovering the noble metaltherefrom; and recovering the organic promoter by extracting it withhalogenated hydrocarbons and evaporating said halogenated hydrocarbons.5. A process as claimed in claim 4 wherein the distillation residue iswater treated at 40° to 80° C.
 6. A process as claimed in claim 4wherein 10 to 100 parts by weight water are used per part by weightdistillation residue.
 7. A process as claimed in claim 4 wherein thequaternary organophosphorus compounds are recovered from their aqueoussolution by extraction with methylene chloride or chloroform.